Abdominal compressions during cardiopulmonary resuscitation: a scoping review

ABSTRACT Objectives: to map the scientific evidence on the use of abdominal compressions during cardiopulmonary resuscitation in patients with cardiac arrest. Methods: this is a scoping review based on the question: “What is the evidence regarding the use of abdominal compressions during cardiopulmonary resuscitation in patients with cardiac arrest?”. Publications up to August 2022 were collected from eight databases. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews was used. Results: seventeen publications were included. The identified general population consisted of adults and elderly individuals. The primary outcome revealed significant rates of return of spontaneous circulation. Secondary outcomes indicated a significant improvement in heart rate, blood pressure, oxygen saturation, and other outcomes. Conclusions: abdominal compressions have been shown to be beneficial. However, further clinical studies are needed to identify the best execution method and its impacts.


INTRODUCTION
In recent years, alternatives to conventional manual Cardiopulmonary Resuscitation (CPR) have been applied with the aim of increasing perfusion during resuscitation attempts after cardiac arrest and improving patient survival.One of these possibilities is the inclusion of manual abdominal compressions as opposed to the rhythm of chest compressions (1) .
One of the techniques for abdominal compression is Interposed Abdominal Compression CPR (IAC-CPR), which requires the presence of three rescuers and involves a combination of conventional chest compression with intermittent abdominal compression.One rescuer compresses the abdomen, another compresses the chest, and the third provides ventilation (2) .
To correctly execute the technique, the professional responsible for abdominal compressions must compress this area at the beginning of the relaxation phase of chest compression, at an intermediate location between the xiphoid process and the navel.The hand position, depth, rhythm, and frequency of abdominal compressions are similar to chest compressions, and the required force is similar to that used for palpating the abdominal aorta (3) .
Studies indicate that when the described IAC-CPR technique is applied, positive effects occur in the patient's hemodynamics during and after resuscitation, compared to standard CPR (3)(4) .These effects include improvement in oxygen metabolism parameters and arterial blood gas levels 30 minutes after the arrest (3) .Additionally, it is effective in treating patients with sudden cardiac arrest who have contraindications for chest compressions (4) .
Considering the listed benefits of IAC-CPR, the American Heart Association Guidelines for Emergency Cardiovascular Care indicate that IAC-CPR is a useful method in CPR, provided there is sufficient trained personnel available, as late or incorrect practice can impair the entire management of cardiac arrest (5) .
Thus, there is evidence of benefits and a recommendation for the practice of IAC-CPR by competent bodies.However, in the guidelines, its level of evidence is categorized as Class IIb (5) , meaning that although not strongly recommended, IAC-CPR has more positive aspects than negatives.Its application in daily practice is limited by the need for trained and qualified professionals.
Despite the classification in the guidelines regarding the use of IAC-CPR, this study becomes relevant as it is necessary to disseminate all evidence regarding the application of this technique through scientific publications.Therefore, mapping this evidence is an advantageous option, providing healthcare professionals with an overview of the possibilities of using this technique.This can favor patient care in cardiac arrest situations that would benefit from the use of this strategy, contributing to increased survival rates for this target population.
It should be noted that, despite a systematic search in the relevant scientific literature, no publications were identified that presented a synthesis of the available evidence in the literature on the use of abdominal compressions in CPR.

OBJECTIVES
To map the scientific evidence on the use of abdominal compressions during cardiopulmonary resuscitation in patients with cardiac arrest.

Ethical Aspects
As the study did not involve human subjects, it was not submitted to the research ethics committee.It should be noted that the study adhered to the ethical and legal principles of Resolution 510/2016 of the National Health Council, which applies to research involving public domain content (6) .

Study design, period, and location
A scoping review was chosen as the approach for this study, as it aims to synthesize evidence from research, categorize, or group existing literature in a specific field in terms of its nature, characteristics, and volume (7) .The theoretical framework of the Joanna Briggs Institute Reviewer's Manual proposed in 2020 was used as a guide for the methodological description (7) .The study protocol was registered in the Open Science Framework under registration osf.io/mdafu.Data were collected from publications up to August 2022, searched during the period from July to August 2022.

Population or sample
From the database searches, a sample of 699 publications was identified, of which 467 were excluded for not meeting the inclusion criteria, 88 for not addressing the central question, and 107 for being duplicate studies, resulting in a total of 17 articles in the final sample.The study population was determined to be patients with cardiac arrest.

Inclusion and exclusion criteria
All published articles that addressed the research question were included, with no language or time period restrictions.Only studies with specific contexts, such as research with animals, comments, news, expert consensus, and articles not published in full, were excluded.

Study protocol
To formulate the research question, the P-C-C strategy (8) was used, where "P" represents the population/participants (patients with cardiac arrest), "C" represents the concept to be investigated (abdominal compressions), and "C" represents the context (cardiopulmonary resuscitation).The established research question was: "What is the evidence on the use of abdominal compressions during cardiopulmonary resuscitation in patients with cardiac arrest?".
Before defining the search terms, a search was conducted in the PubMed database to identify the most frequently used descriptors and keywords in studies related to the topic of interest.Thus, the following search strategy was developed, crossing the PCC strategy terms with boolean connectors AND and OR, as described in Chart 1.
The search for studies was conducted independently by two researchers, and in case of disagreement, a third researcher made the final decision.
After the study selection, duplicate publications were identified and excluded.Subsequently, the eligibility evaluation process began, with screening of the studies through the reading of titles and abstracts.Later, the full text of the selected studies was read to confirm eligibility and ensure the inclusion of relevant studies on the subject.It is worth noting that any inconsistencies or doubts in this process were resolved through consensus and discussion among the authors and other reviewers, if necessary.
The data from the articles were independently mapped using a standardized electronic form.Data were collected on the study type, design, and country; population characteristics; setting; events, rhythm, or cause of cardiac arrest; intervention; and outcomes.Additionally, the studies were classified with a level of evidence and strength of recommendation, following Oxford recommendations (9) .The data were then tabulated for presentation, as appropriate.

Analysis of results and statistics
The data were compiled and tabulated in a spreadsheet using Excel 2016, and statistical analysis, including percentage calculations, was performed for a consistent presentation of the evidence.The results were presented in the form of two tables: one providing a description of the selected articles and the other mapping the scientific evidence on the use of abdominal compressions during cardiac arrest.
The scoping review was conducted following the PRISMA extension for scoping reviews (PRISMA-ScR) (10) .

RESULTS
At the end of the search, 17 articles were left, with 13 of them extracted from Pubmed/Medline, and one each from Pubmed/ PMC, Scopus, Embase, and Web Of Science, respectively.The flowchart of the searches is described in Figure 1.
The articles included in the study covered the period from 1984 to 2022.Among them, seven (41.2%) were published in the 2000s, while ten (58.8%) were from the 1980s and 1990s, respectively.Regarding the origin of the publications, eight (47%) were from the United States of America (USA), three (17.6%)from China, two (11.8%) from California, two (11.8%) from Iran, and one (5.9%) each from Spain and Italy.As for the methodological approach, there was a predominance of 11 publications (64.7%) of prospective studies comparing case and control groups.All the research (100%) was conducted with adults in cardiac arrest, with an average age ranging from 54 to 85 years, as described in Chart 2.
The mapping of scientific evidence identified various mechanisms and protocols involving the use of abdominal compressions.In the primary outcome, 13 studies described the return of spontaneous circulation.Among these, nine (69.2%) reported a significant improvement in patients who received abdominal compressions.Ten secondary outcomes related to the return of spontaneous circulation were also identified.The data are detailed in Chart 3.

DISCUSSION
The analysis of the study allowed us to identify that research on the use of abdominal compression during CPR is not recent, as it dates back from 1984 to 2022.Among these, ten (62.5%) were conducted in the 1980s and 1990s.However, the American Heart Association (AHA) has not yet introduced this technique into the standard resuscitation protocol (27) .
In China, in 2016, the Specialized Committee of Cardiopulmonary Resuscitation of the Chinese Hospital Research Association discussed with researchers and experts the adoption of cardiopulmonary resuscitation using abdominal compressions through clinical practice (25) .
According to Wang et al. (28) , for the incorporation of abdominal compressions into CPR protocols, studies that explore the standardized and diversified methods currently available are needed.In this context, the present study identified the presence of three distinct protocols using abdominal compressions: CPR with elevation and abdominal compression, CPR with simultaneous abdominal and chest compressions, and CPR with interposed chest and abdominal compression (CTAI).("heart arrest" OR "death, sudden, cardiac" OR "cardiac arrests" OR "cardiopulmonary arrest" OR "sudden death" OR "cardiopulmonary resuscitation" OR "basic life support" OR "advanced life support" OR "fist aid" OR "basic cardiac life support" OR "cpr" OR "cardio-pulmonary resuscitation" OR "life support, basic cardiac" OR "heart massage" ) AND ("abdominal compression" OR "abdominal compressions" OR "adbomen" OR "abdominal lifting" OR "abdominal compression decompression")

Mechanism for performing abdominal compressions
Abdominal compressions are carried out using a mechanical device comprising three components: a display panel, pressure application handles, and a negative pressure device.Manual abdominal compressions.

Protocol 1: CPR with Elevation and Abdominal Compression
-Identification of cardiac arrest following the AHA protocol (unconscious victim, no pulse, no breathing, or agonal breathing).
-Abdominal compressions are performed using the mechanical device.The depth, rate, and frequency of abdominal compressions adhere to the same guidelines as AHA-recommended chest compressions (24)(25)(26) .
-The duration of compression and elevation is defined in a 1:1 ratio (26) .
-The applied compression force is approximately 186 mmHg, and the elevation force is approximately 112 mmHg (2) .
-Medications are administered following the current AHA protocol at the time of the study (24) .

Protocol 2: CPR with Simultaneous Abdominal and Thoracic Compressions
-Identification of cardiac arrest following the AHA protocol (unresponsive victim, no pulse, no breathing, or gasping breathing).
-The protocol was initiated 2 minutes after the cessation of aortic pressure (16) .
-Thoracic compression was carried out using an external device with parameters in accordance with the AHA guidelines at the time.A slightly inflated blood pressure cuff was placed over the mesogastric area.A mercury column was attached to the cuff.The abdominal compressions had a pressure of 100 mmHg during the relaxation phase of the chest (16) .
-The depth, rate, and frequency of abdominal compressions follow the rhythms of chest compressions indicated by the AHA at the time of the study (17)(18)(22)(23)25) .
-Healthcare professionals positioned their hands on the victim's abdomen.The base of the hands was placed about 3 cm to the left of the midline, and the fingers supported gently on the abdomen.With this positioning, the abdomen was compressed using the hypothenar and thenar regions of the hands along a craniocaudal line of the abdominal aorta (22) .
-Abdominal compressions were performed to the left of the midline to preferentially compress the abdominal aorta and minimize compression of the vena cava (15,(19)(20) .
-Abdominal compressions were performed with the hands open, one on top of the other, centered over the umbilicus (11,13,(17)(18) , between the xiphoid process and the umbilicus (24) , or in the epigastric region (11) .
To be continued Among the identified techniques, the Brazilian Society of Cardiology, through the Guideline on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care from 2013 to 2019, describes the use of auxiliary maneuvers during CPR, with CTAI standing out.According to experts, many efforts have been made by researchers in the last three decades to search for alternative techniques to standard CPR, and CTAI is a recommended technique in a hospital setting with a trained team.This alternative method involves three rescuers responsible for chest compression, abdominal compression, and ventilation, respectively.The authors emphasize that this alternative technique should take into consideration external (place of care) and internal (clinical condition of the patient) aspects (29)(30) .
Such information corroborates with the results of the present study since the research conducted, so far, contraindicated patients with a history of abdominal diseases or suspected pregnancy.Due to the risk of worsening the clinical condition, it is unethical to include these participants in the studies, as both national and international guidelines and regulatory norms for research involving humans recommend that the study benefits should outweigh the risks (31)(32) .
Furthermore, the relevance of implementing alternative techniques to standard CPR is highlighted because, according to Chinese researchers, the usual technique is not effective for patients with rib fractures, chest deformity, or clinical conditions of hemothorax and pneumothorax (26) .A study conducted in Germany with 22,565 trauma patients identified that the spontaneous circulation return rate was present in only 11% of patients who received standard CPR (33) .
Thus, it is believed that the use of abdominal compressions may be an alternative option to standard CPR for adults aged 18 years and older with non-traumatic cardiac arrest.It is noteworthy that the mapping conducted identified that eight studies reported the return of spontaneous circulation in patients who received abdominal compressions, while three did not identify a statistical difference when compared to patients who received only standard CPR.
In addition to the return of spontaneous circulation, the present study identified the presence of secondary outcomes: significant improvement in heart rate, blood pressure, oxygen saturation, 24hour survival after resuscitation, increased expired carbon dioxide (CO2), higher hospital discharge rate, and absence of vomiting.
The reasons for the improvement in patients' clinical conditions were described in 2016 by researchers from Iran.According to the authors, 20% of the blood volume is located in the abdomen.Rhythmic compressions can result in increased venous return and cardiac preload.Additionally, during the diastolic phase of chest compressions, coronary perfusion occurs.Thus, abdominal compressions during the diastolic phase increase blood flow to the heart (1) .
Similarly, the CTAI technique was compared using a concentrated parameter mathematical model in patients with a single ventricle shunt, which corresponds to a congenital heart disease of unique physiology, in which it is extremely difficult to resuscitate due to severe hypoxemia during CPR.Thus, Stromberg et al. (2022) (34) evidenced that the use of this technique contributes to increased pulmonary blood flow, cardiac output, blood pressure, coronary perfusion pressure, and coronary blood flow, compared to standard CPR.
Another benefit evidenced in the application of CTAI would be the reduction in the incidence of gastric inflation (35) , which could result in a decrease in rare complications of pneumoperitoneum that lead to gastric perforation, where most require laparotomy for correction.The aforementioned complication occurs due to the accumulation of air in the abdominal cavity, as a consequence of inadequate airway management and inadequate technique of

Primary Outcome
Secondary Outcome -Abdominal compression and elevation had a statistically significantly higher restoration of spontaneous circulation compared to the rate of chest compression [(p < 0.01) (25) , (p= 0.049) (24) ].
-Regurgitation did not occur in any patients (12)(13) .conventional CPR compressions (36)(37) .Thus, there is growing evidence of positive outcomes regarding the effectiveness and usability of CTAI, although it remains limited by its technical difficulty (35) .These data emphasize the need for studies that assess the best abdominal compression technique since the studies conducted so far have reported different abdominal compression techniques, including compressions performed to the left of the midline to preferentially compress the abdominal aorta and minimize compression of the vena cava (15,(19)(20) , and abdominal compressions performed with open hands, one over the other, centered over the umbilicus (11,13,(17)(18) , between the xiphoid and the umbilicus (2) , or in the epigastric region (12) .

Indications
In addition to the different abdominal compression techniques, it is necessary to identify the most effective force during resuscitation since the lack of standardization of the pressure exerted by the rescuers' hands was one of the limitations of the studies conducted so far (17,2) .These data reinforce the need for new studies that contribute to the elaboration of a standard protocol for the use of abdominal compressions during cardiac arrest, in order to favor the improvement in the quality of care provided during this clinical emergency episode.

Study Limitations
A limitation of the study is the exclusion of articles not published in full.This might exclude more recent research that is not yet fully available in the literature and could present new results regarding the use of abdominal compressions during CPR.

Contributions to Nursing, Healthcare, or Public Policy
The present study provides benefits to the scientific community, nurses, and other healthcare professionals.The mapping of the main scientific evidence allowed for identifying the state of the art in using abdominal compressions during CPR.It includes information on the mechanisms of abdominal compression, the studied protocols, primary and secondary outcomes of applying this technique, indications, and contraindications, as well as eligibility criteria and the main limitations of the conducted studies.
This mapping serves as a scientific basis for recognizing this technique as an alternative to standard CPR in patients with a favorable clinical condition.Moreover, it supports the conduction of new studies aiming to explore the scarce information in the scientific literature.

CONCLUSIONS
The majority of the studies identified that the return of spontaneous circulation in the group that received abdominal compressions is significantly higher than in the standard CPR group.Regarding secondary outcomes, the publications indicated significant improvements in heart rate, blood pressure, oxygen saturation, 24-hour survival after resuscitation, increased expired CO2, higher hospital discharge rate, and absence of regurgitation.Additionally, the studies that analyzed the bodies of non-surviving patients found no injuries in the abdominal organs.
None of the researchers contraindicated this technique.However, despite the findings, three studies did not find a statistical difference when comparing standard CPR with CPR with abdominal compression.
Finally, there is a need for new randomized clinical trials that evaluate the most effective protocol for CPR with abdominal compression and the best techniques for compressing the abdomen.Additionally, new studies should try to address the limitations of the already published studies, thus conducting research to evaluate long-term survival rates and performing autopsies on the bodies of non-surviving patients becomes necessary.

CONTRIBUTIONS
Lima MMS, Ximenes MAM, Araújo DV, Barros LM, Galindo Neto NM and Caetano JA contributed to the conception or design of the study/research.Lima MMS, Ximenes MAM, Araújo DV, Barros LM, Galindo Neto NM and Caetano JA contributed to the analysis and/or interpretation of data.Lima MMS, Ximenes MAM, Araújo DV, Barros LM, Galindo Neto NM and Caetano JA contributed to the final review with critical and intellectual participation in the manuscript.